1. Field of Invention
The present invention is in the field of wire antennas, and more specifically provides a versatile wire antenna that can be up to 80 percent shorter than traditional wire antennas—while still providing exceptional operating characteristics. The present invention is also more durable than traditional wire antennas, offers broadband and multi-band performance, eliminates tension on the wire components, does not require inductive elements, does not require end insulators or transmission-line feed-point insulators, has low noise characteristics, and offers the potential for significant static-discharge capability.
2. Description of Related Art
Antennas made of wire are the oldest type of antenna system. They are generally easy to construct, but, particularly on frequencies below VHF (below 30 MHz), their required length can be inconvenient or not practical for the space available for their construction and use.
A common wire antenna used on frequencies below 30 MHz is called a “dipole”, in which equal lengths of wire (typically copper wire) are fed by a two-conductor RF transmission line (such as coaxial cable) at a wire junction typically comprised of a ceramic insulator. The combined length of the two wire components is traditionally determined by the formula 468/f, where f is the desired resonance frequency in megahertz and the resultant length is in feet.
For example, for an antenna to be resonant on 3.755 MHz, a frequency in a popular amateur “ham” radio band, the overall length of the wire needed would be approximately 124.6 feet (468 divided by 3.755). In a classic dipole configuration, this length of wire would be divided in two (62.3 feet for each wire radiator) and fed by a two-conductor transmission line. To suspend the wire elements, the far end of each end-point of wire would be attached to insulators, usually made of ceramic or plastic. The insulators would then be fastened to lengths of rope. The rope ends would then typically be fed through pulleys attached to support structures; tension would be applied to the overall rope-and-wire system to create a horizontal antenna system.
One unavoidable problem with this type of antenna is that tension is created throughout the entire system, including the wire elements. Over time, it is common for the wire to stretch and break—and thus requiring the wire element(s) to be repaired or replaced.
Another problem with a common dipole antenna is the overall length required. In the above example, a radio operator may not have the 124.6 feet necessary on his or her property to suspend the dipole. Apartment dwellers and homeowners with small properties may be particularly challenged to find the 124.6 feet of horizontal space without impinging on neighbors' properties.
As inadequate horizontal space is such a common problem, a number of options have been developed to modify a dipole to function at a shorter-than-natural resonant length.
One shorter-length option is to include what is commonly referred to as “loads” in the lengths of wire; these loads are typically comprised of coils and capacitors that electrically simulate a longer length of wire. However, the efficiency and performance of “loaded dipoles” is significantly less than full-length dipoles.
Another shorter-length option is something called a “slinky antenna”—whereby the wire of the antenna is literally made of a child's Slinky toy, which is essentially a coil of spring metal. There are numerous problems and deficiencies with the slinky antenna. One such deficiency is that slinky coils are not ordinarily created by the end-user; the coiling process of the spring steel is beyond the means of most people. Another deficiency is that the slinky antenna can typically only be stretched out to approximately 15 feet without permanently deforming the slinky coil. Other common and reported deficiencies include that the resonance, impedance, and standing-wave ratio (SWR) characteristics of the slinky antenna tend to change when wet. Another deficiency of the slinky antenna is the inherent in the coil itself, as the antenna radiators are essentially large helical inductors which provide unusual and inefficient RF transmission and reception characteristics. All in all, due to these and other deficiencies, the slinky antenna has never gained wide acceptance in the RF-transmission community.
Given the above issues with shortened wire antennas, it would be a great advantage to an antenna user if an antenna could be made shorter and resonant—without “loads” or slinky-like coils. It would be a further great advantage if the antenna can be strung without the wire, itself, bearing the tensile load of the tensioning necessary to keep the wire taut.